Up until very recently I was still using lead solder, and some unlabelled solid flux paste when necessary (borrowing both from my parents). I don't have much of a steady hand, and my joints didn't look too good, but they worked.

I recently bought some new lead-free solder (96% tin 4% silver, it says), plus a temperature controlled iron with a finer tip. And I thought I should also replace the flux, since the old stuff has no indication of what's in it and could be pretty toxic too. So I got the Circuitworks no-clean flux pen. (The tip wasn't quite what I expected, and maybe I'm not applying enough of the stuff, which could be part of this.)

So I started using my new items and it wasn't working at all. The solder just didn't want to stick to anything, and when it did stick, it was coming up rough and grey and not very strong. I tried adjusting the temperature both ways, without much luck. Eventually I tried using the old flux paste again, and it started to work, but I seem to be needing rather a lot of it. And even when I've tinned the two parts, they seem to want more flux before they'll stick together, which is something I've never seen before. (I've only *had* to use the separate flux when tinning objects that weren't exactly designed to be soldered, though sometimes I used it anyway to make things easier.)

Any ideas what's happening here? I've read that lead-free solder is "more difficult", but I didn't expect it to be quite this bad

When I wipe the tip, it comes up shiny like the lead solder did (and at that point I'd say it looked well tinned and clean), but it seems to get dirty again within a few seconds.

I guess some of this is normal then? Maybe I'm just unskilled.

Is it true that tin/silver is easier to use than tin/copper? Because I spent a bit extra on that. It's supposed to "flow better" or something. I couldn't find much about that when I tried to research it though.

Also, what happens if the two kinds of solder get mixed together? I need to keep one tip free of lead for actual lead-free use, but in regular work I can see a few situations where that might arise.

The temperature scale is not graduated - I just have to guess at first, but once I've got it right once, I can put it back in the same place the next time.

You may be right about my tip being too fine. My last question comes into play here - if lead contamination isn't going to mess up it's physical properties, I could try it on the old iron for comparison. There are many tips available for my new one but it looks like changing them is a lot of effort. It says they must only be changed cold, so changing in the middle of a job would be annoying!

- if lead contamination isn't going to mess up it's physical properties, I could try it on the old iron for comparison.

Click to expand...

Dont worry, if you wipe the old tip, "contamination" will be very slight and the whole issue of banning lead is just to keep people from its adverse affects and since you've probably melted several pounds of lead during soldering, less than a mg ain't gonna hurt

Even if you don't know the setting of your iron, just turn it up until it works - personally, I'm not giving up leaded solder until I cannot get it anymore, although I prefer the kind with a dab of silver in it, since it wet the material so much better and gives a more shiny result.
It needs a bit higher temperature as well, but since I mostly use #8 bits on my WTCP50, that's really not an issue (Weller tips are numbered in amounts of a hundred degree Fahrenheit, so this is 800°F or 427°C).

Melts 30 degrees (F) higher than lead/tin and can use the same rosin flux. Use a wet sponge to wipe the tip and use extra rosin flux to help you with the soldering.
Rosin solder is brown, if the stuff you were using was white it may have been plumbing flux and is corrosive.

Thanks for the info. The flux paste is brown, and I'm sure it's supposed to be soldering flux - if rosin flux hasn't changed in a long time, maybe it's still the right thing.

I think the Circuitworks flux might work if I could just get enough of it on - I'd probably dismantle the pen if I was sure I could do it without getting the stuff everywhere. A soft brush would work much better than that hard pen-tip.

I put a thicker tip on my soldering iron, and it's working much better. The blobs of solder are coming up properly shiny, and I'm only needing to flux the pieces before I tin them- two tinned parts will now stick together with little effort. So, thanks n9352527.

In another topic, it was suggested that I use a fine tip for SMD soldering and other such small fiddly things. But it looks like my fine tip is not going to work. (I guess I'll try the fine tip with the lead solder to see how that is, but I may be wanting to build a lead-free item at some point, so that would only help for personal-use projects.)

Also, I'm still wondering about the different lead-free solder mixtures. Is there much to choose between them?

Also, I'm still wondering about the different lead-free solder mixtures. Is there much to choose between them?

Click to expand...

Yes, there is, from a technical perspective. The most common right now are the Sn-Cu-Ag types. THey "kind of" come the closest to the tin-lead solders in terms of balancing strength, melting temperature, and wettability...althought they are still quite inferior in those aspects. I personally use the 95Sn5Sb solder but it's what I have lying around and it's a bitch to work with...probably because the iron right now I have isn't temperature controlled and isn't fine enough to make proper contact with the size of the things I am working with.

I am thinking about switching back to lead-tin...I already wear a respirator and conformal coat my boards anyways, and just basically need to make sure I have all the right dedicated tools to come in contact with the solder, so I don't have to touch it with my hand and then touch something else to "spread it around"- which was the whole problem I switched in the first place (I'm pretty sure I have a form of OCD that's off for most of the time but kicks into really high gear when it comes to spreading lead around). I end up having a need to scrub down the the area, tools, and everything my hands and the tools touched.

There are some strange solders. An iridium one that's 600 per ounce and you'd swear a good connection is bad. It was used because it can flex almost like rubber without breaking.

I've used high temp solders that never give what looks like a good connection. You have to go by shape and smoothness.

Several companies had worked on conductive glues but no product ever came of it. Recently one compan stated it's working on a conductive nanoparticle glue that acts almost like a solder as it will melt and flow with heat then hardens into permanence.